Thermobaric weapons are able to overcome shortcomings of conventional blast/fragmentation and shaped-charge munitions with respect to certain targets. For example, conventional hard-target penetrating fragmentation bombs have shown shortcomings for defeating tunnels and caves. Fragments can be stopped by walls and do not necessarily penetrate through a containment system. By contrast, blast waves can travel around corners and their effects are not based on penetration. Conventional countermeasures such as physical barriers (e.g. sandbags) and personnel armor are not especially effective against thermobaric weaponry.
Detonation of a high explosive device produces a rapid, localized energy release. This energy is dissipated by the formation of a blast wave, thermal radiation, and the breakup of the munition casing and acceleration of the fragments. Thus, in conventional blast/fragmentation warheads, a large part of the initially released energy is consumed by the breakup of the casing and acceleration of the resulting fragments. By contrast, thermobaric weaponry usually employs relatively thin casings, and most of the released energy ends up as a fireball and a blast/shock wave. The level of structural damage and injury caused by the blast is dependent on peak pressure, impulse (a function of time and pressure), and the overall shape of the pressure-time curve.
FIG. 1 is a plot of blast overpressure versus duration required to produce lethal/severe damage upon an unprotected 70 kg soldier. As evidenced by the plot depicted in FIG. 1, overpressure duration on the order of 2-20 milliseconds (ms) results in the greatest probability of inflicting lethal or severe damage. Generally speaking, the longer a given overpressure is sustained, the lower the peak pressure necessary to achieve an equivalent disruptive or lethal effect. However, as evident from FIG. 1, this is not a linear relationship.
Thermobaric or enhanced blast munitions exploit secondary combustion of explosives as a source of lethal energy. In conventional systems, energy dense fuels, such as aluminum powder, have been added into an organic explosive. However, such metal powders burn relatively slowly such that while some energy is released in the 2-10 ms time frame, much of their energy is released at a later time after the initial pressure spike, and thus does not optimally contribute to sustaining a high positive impulse.
Relevant publications include U.S. Pat. Nos. 5,717,159; 5,912,069; 6,679,960 B2; and 6,843,868 B1, the entire disclosure of each of these publications is incorporated herein by reference.